Changes of temperature and light significantly influence the growth and activity of phytoplankton. To explore the effects of these two variables on the cyanobacterial blooms, we analyzed the growth of Microcystis aeruginosa and Scenedesmus obliquus, as well as the competition between the two species, under conditions of low temperature and low light, and under conditions of release from these two stress factors. The results showed that low temperature and low light significantly inhibited the growth of microalgae. Low temperature led to a stronger inhibitory effect on M. aeruginosa than low light did; however, the growth inhibition of S. obliquus was more sensitive to low light than to low temperature. After release from low temperature or limiting light, all of the experimental taxa exhibited the overcompensation growth within a limited time and this response varied by species. Two M. aeruginosa strains showed a greater response to increased temperature than increased light. However, overcompensation of S. obliquus was greater in response to increased light than increased temperature. When the species were grown together, results showed that under all culture conditions, the toxic Microcystis strains (912) had a competitive advantage over S. obliquus. Although there was no significant difference between the competitive ability of the nontoxic Microcystis strain (469) and S. obliquus under the normal, the former (469) showed a competitive disvantage to S. obliquus under conditions of release from low light and low temperature. Chlorophyll-a content of all experimental algae overcompensated when released from light limitation. In the temperature experiments, the increase of chlorophyll-a content and algal density were asynchronism for all species, and cryogenic pre-treatment had a negative after-effect on microalgae chlorophyll-a content under release from low temperature. The response of dehydrogenase activity of algae when released from low temperature or low light stress varied with algae species, and the compensating increase of dehydrogenase activity of toxic strains (912) was significantly higher than that of the other two taxa. The results suggested that higher the compensatory growth of toxic Microcystis as well as its competitive advantage over S. obliquus while released from low temperature and light stresses, might be the important mechanisms that result in blue-green algae bloom.